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Soluble aggregates of the amyloid-beta peptide are trapped by serum albumin to enhance amyloid-beta activation of endothelial cells.

Reyes Barcelo AA, Gonzalez-Velasquez FJ, Moss MA - J Biol Eng (2009)

Bottom Line: Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates.These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses.These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, University of South Carolina, 2C02 Swearingen Engineering Center, Columbia, South Carolina 29208, USA. Adriana.ReyesBarcelo@kraft.com

ABSTRACT

Background: Self-assembly of the amyloid-beta peptide (Abeta) has been implicated in the pathogenesis of Alzheimer's disease (AD). As a result, synthetic molecules capable of inhibiting Abeta self-assembly could serve as therapeutic agents and endogenous molecules that modulate Abeta self-assembly may influence disease progression. However, increasing evidence implicating a principal pathogenic role for small soluble Abeta aggregates warns that inhibition at intermediate stages of Abeta self-assembly may prove detrimental. Here, we explore the inhibition of Abeta1-40 self-assembly by serum albumin, the most abundant plasma protein, and the influence of this inhibition on Abeta1-40 activation of endothelial cells for monocyte adhesion.

Results: It is demonstrated that serum albumin is capable of inhibiting in a dose-dependent manner both the formation of Abeta1-40 aggregates from monomeric peptide and the ongoing growth of Abeta1-40 fibrils. Inhibition of fibrillar Abeta1-40 aggregate growth is observed at substoichiometric concentrations, suggesting that serum albumin recognizes aggregated forms of the peptide to prevent monomer addition. Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates. Such partial inhibition of Abeta1-40 aggregation leads to an increase in the ability of resulting aggregates to activate endothelial cells for adhesion of monocytes. In contrast, Abeta1-40 activation of endothelial cells for monocyte adhesion is reduced when more complete inhibition is observed.

Conclusion: These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses. These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

No MeSH data available.


Related in: MedlinePlus

Effect of BSA inhibition of Aβ1–40 monomer aggregation on endothelial adhesion in HBMVECs. HBMVEC monolayers grown to confluence in 96-well plates were stimulated via 24 h incubation. Confluent monolayers were incubated alone (-CONT) or with 5 μM Aβ1–40 aggregates formed in the absence (+CONT) or presence of BSA at concentrations 2-fold (BSA, 2X) or 4-fold (BSA, 4X) in excess of Aβ1–40 monomer. Activated monolayers were washed and adhesion of Calcein-labelled THP-1 cells (2 × 104 cells/well) was assessed via fluorescence as described in Materials and Methods. * p < 0.05, ** p < 0.01, *** p < 0.001. Results are representative of three independent experiments performed with six repetitions. Error bars represent SEM.
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Figure 3: Effect of BSA inhibition of Aβ1–40 monomer aggregation on endothelial adhesion in HBMVECs. HBMVEC monolayers grown to confluence in 96-well plates were stimulated via 24 h incubation. Confluent monolayers were incubated alone (-CONT) or with 5 μM Aβ1–40 aggregates formed in the absence (+CONT) or presence of BSA at concentrations 2-fold (BSA, 2X) or 4-fold (BSA, 4X) in excess of Aβ1–40 monomer. Activated monolayers were washed and adhesion of Calcein-labelled THP-1 cells (2 × 104 cells/well) was assessed via fluorescence as described in Materials and Methods. * p < 0.05, ** p < 0.01, *** p < 0.001. Results are representative of three independent experiments performed with six repetitions. Error bars represent SEM.

Mentions: When HBMVEC monolayers were treated with 5 μM Aβ1–40 aggregates formed in the absence of BSA, a 2.3-fold increase in adhesion of THP-1 monocytes relative to untreated control monolayers was observed (Figure 3). This result is similar to that reported previously [6]. Aβ1–40 aggregates formed in the presence of a 2-fold excess of BSA stimulated an even more pronounced 2.9-fold increase in adhesion of THP-1 monocytes, despite the decreased thioflavin T fluorescence observed under these aggregation conditions (Figure 1). In contrast, when Aβ1–40 aggregates were formed in the presence of a 4-fold excess of BSA, a smaller increase in THP-1 adhesion of only 1.5-fold was observed. BSA treatment of endothelial monolayers in the absence of Aβ made an insignificant contribution to the observed changes in adhesion. These results demonstrate that inhibition of in vitro Aβ1–40 monomer aggregation by BSA is not paralleled by a dose-dependent decrease in physiological activity.


Soluble aggregates of the amyloid-beta peptide are trapped by serum albumin to enhance amyloid-beta activation of endothelial cells.

Reyes Barcelo AA, Gonzalez-Velasquez FJ, Moss MA - J Biol Eng (2009)

Effect of BSA inhibition of Aβ1–40 monomer aggregation on endothelial adhesion in HBMVECs. HBMVEC monolayers grown to confluence in 96-well plates were stimulated via 24 h incubation. Confluent monolayers were incubated alone (-CONT) or with 5 μM Aβ1–40 aggregates formed in the absence (+CONT) or presence of BSA at concentrations 2-fold (BSA, 2X) or 4-fold (BSA, 4X) in excess of Aβ1–40 monomer. Activated monolayers were washed and adhesion of Calcein-labelled THP-1 cells (2 × 104 cells/well) was assessed via fluorescence as described in Materials and Methods. * p < 0.05, ** p < 0.01, *** p < 0.001. Results are representative of three independent experiments performed with six repetitions. Error bars represent SEM.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2683804&req=5

Figure 3: Effect of BSA inhibition of Aβ1–40 monomer aggregation on endothelial adhesion in HBMVECs. HBMVEC monolayers grown to confluence in 96-well plates were stimulated via 24 h incubation. Confluent monolayers were incubated alone (-CONT) or with 5 μM Aβ1–40 aggregates formed in the absence (+CONT) or presence of BSA at concentrations 2-fold (BSA, 2X) or 4-fold (BSA, 4X) in excess of Aβ1–40 monomer. Activated monolayers were washed and adhesion of Calcein-labelled THP-1 cells (2 × 104 cells/well) was assessed via fluorescence as described in Materials and Methods. * p < 0.05, ** p < 0.01, *** p < 0.001. Results are representative of three independent experiments performed with six repetitions. Error bars represent SEM.
Mentions: When HBMVEC monolayers were treated with 5 μM Aβ1–40 aggregates formed in the absence of BSA, a 2.3-fold increase in adhesion of THP-1 monocytes relative to untreated control monolayers was observed (Figure 3). This result is similar to that reported previously [6]. Aβ1–40 aggregates formed in the presence of a 2-fold excess of BSA stimulated an even more pronounced 2.9-fold increase in adhesion of THP-1 monocytes, despite the decreased thioflavin T fluorescence observed under these aggregation conditions (Figure 1). In contrast, when Aβ1–40 aggregates were formed in the presence of a 4-fold excess of BSA, a smaller increase in THP-1 adhesion of only 1.5-fold was observed. BSA treatment of endothelial monolayers in the absence of Aβ made an insignificant contribution to the observed changes in adhesion. These results demonstrate that inhibition of in vitro Aβ1–40 monomer aggregation by BSA is not paralleled by a dose-dependent decrease in physiological activity.

Bottom Line: Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates.These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses.These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, University of South Carolina, 2C02 Swearingen Engineering Center, Columbia, South Carolina 29208, USA. Adriana.ReyesBarcelo@kraft.com

ABSTRACT

Background: Self-assembly of the amyloid-beta peptide (Abeta) has been implicated in the pathogenesis of Alzheimer's disease (AD). As a result, synthetic molecules capable of inhibiting Abeta self-assembly could serve as therapeutic agents and endogenous molecules that modulate Abeta self-assembly may influence disease progression. However, increasing evidence implicating a principal pathogenic role for small soluble Abeta aggregates warns that inhibition at intermediate stages of Abeta self-assembly may prove detrimental. Here, we explore the inhibition of Abeta1-40 self-assembly by serum albumin, the most abundant plasma protein, and the influence of this inhibition on Abeta1-40 activation of endothelial cells for monocyte adhesion.

Results: It is demonstrated that serum albumin is capable of inhibiting in a dose-dependent manner both the formation of Abeta1-40 aggregates from monomeric peptide and the ongoing growth of Abeta1-40 fibrils. Inhibition of fibrillar Abeta1-40 aggregate growth is observed at substoichiometric concentrations, suggesting that serum albumin recognizes aggregated forms of the peptide to prevent monomer addition. Inhibition of Abeta1-40 monomer aggregation is observed down to stoichiometric ratios with partial inhibition leading to an increase in the population of small soluble aggregates. Such partial inhibition of Abeta1-40 aggregation leads to an increase in the ability of resulting aggregates to activate endothelial cells for adhesion of monocytes. In contrast, Abeta1-40 activation of endothelial cells for monocyte adhesion is reduced when more complete inhibition is observed.

Conclusion: These results demonstrate that inhibitors of Abeta self-assembly have the potential to trap small soluble aggregates resulting in an elevation rather than a reduction of cellular responses. These findings provide further support that small soluble aggregates possess high levels of physiological activity and underscore the importance of resolving the effect of Abeta aggregation inhibitors on aggregate size.

No MeSH data available.


Related in: MedlinePlus